richedit: Removed some conditions that are always taken.

ME_GetCursorCoordinates had two conditions that were always taken.  The
first condition was if(pCursor->pRun->type == diRun) was following an
assertion making the exact same check.  The next one, if(row), should
always be taken, otherwise the richedit controls are in a corrupt state,
therefore an assertion is more appropriate.